Video – Fixed Background, Movement Overlay

How to overlay several delays of people passing by over the same background, captured by one camera? The idea is that, while the background stays the same, whatever happens over it is multiplied by the number of delay functions running in the patch. The delay part is no problem, but I really have no idea on how to solve having the different figures of people moving over the same background, allowing them to mix transparencies when overlaying but having them as clear as possible when not. Any Idea on how to solve this is welcome.